linux-ext4 - Re: [PATCH 3/4]ext4: Return exchanged blocks count to user space in failure

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Message-ID: <6149e97b0909022213p2b8463fdm796c8687d36ae54c@mail.gmail.com>
Date:	Thu, 3 Sep 2009 13:13:03 +0800
From:	Peng Tao <bergwolf@...il.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
Cc:	Akira Fujita <a-fujita@...jp.nec.com>,
	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 3/4]ext4: Return exchanged blocks count to user space in 
	failure

Hi, Greg,

On Thu, Sep 3, 2009 at 4:59 AM, Greg Freemyer<greg.freemyer@...il.com> wrote:
> Peng,
>
> I have not looked at the code very closely, but can you tell me where
> a file corruption can take place?   Not completing the replacement of
> extents with donor extents is one thing.  Corrupting the original file
> contents is another.
The file corruption is mainly because of the half done replacement.

My test case is here:
http://marc.info/?l=linux-ext4&m=124992522305319&w=2

With Akira's previous patch
(http://marc.info/?l=linux-ext4&m=124937430627867&w=2),
EXT4_IOC_MOVE_EXT does not panic the kernel any more. But it leaves
the orig file's extent tree corrupted.

>
> Clearly we need EXT4_IOC_MOVE_EXT to fail gracefully and not corrupt
> the original file the vast majority of the time.
>
> Greg
>



-- 
Cheers,
Peng Tao
State Key Laboratory of Networking and Switching Technology
Beijing Univ. of Posts and Telecoms.
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